Preparation of high thermal conductivity copper–diamond composites using molybdenum carbide-coated diamond particles

Molybdenum carbide (Mo₂C) coatings on diamond particles were proposed to improve the interfacial bonding between diamond particles and copper. The Mo₂C-coated diamond particles were prepared by molten salts method and the copper–diamond composites were obtained by vacuum pressure infiltration of Mo₂C-coated diamond particles with pure copper. The structures of the coatings and composites were investigated using X-ray diffraction, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. The results indicated that the Mo₂C coatings effectively improved the wettability between diamond particles and copper matrix, and Mo₂C intermediate layers were proved to decrease the interfacial thermal resistance of composites. The thermal conductivity of the composite reached 608 Wm^?1 K^?1 with 65 vol.% Mo₂C-coated diamond, which was much higher than that with uncoated diamond. The greatly enhanced thermal conductivity is ascribed to the 1-μm-thick Mo₂C coatings. Mo₂C coatings on diamond particles are proved to be an effective way to enhance the thermal conductivities of copper–diamond composites.     

Preparation and properties of antioxidative BaO–B<Subscript>2</Subscript>O<Subscript>3</Subscript>–SiO<Subscript>2</Subscript> glass-coated Cu powder for copper conductive film on LTCC substrate

In this study, uniform BaO–B₂O₃–SiO₂ glass coatings on micro Cu powders with different glass/Cu ratio were prepared by sol–gel method. The pastes prepared with the glass-coated Cu powders were screen printed on low temperature co-fired ceramic (LTCC) substrate. Then the dry films on substrate were binder-burned-out at 400 °C in air and co-fired at 910 °C in N₂ atmosphere. During the binder-burning-out process, the oxidization of the films with 9 and 11 wt% glass was slight because of the improvement of oxidization resistance of the glass-coated Cu powders. Moreover, the sintered film with 9 wt% glass coating showed no crystal phase of copper oxide and had small sheet resistance of 1.3 mΩ/□, which can be used as good conductive thick film on LTCC substrate for microelectronic packaging.     

Microstructure and electrical property of copper films on a flexible substrate formed by an organic ink with 9.6 % of Cu content

An organic copper ink with 9.6 wt% of Cu content derived from a short carbon chain organic copper precursor was successfully applied on a modified PI substrate and easily formed a favorable conductive copper film by self-reduction in the sintering process, which showed excellent conductivity. The effects of sintering temperature and time on the microstructure and conductivity action of the copper films were studied by XRD, EDS and SEM and electrical measurements, respectively. The sheet resistance and resistivity were determined to be as low as 0.11 Ω/□ and 2.2 × 10^?5 Ω·cm. The conduction mechanism is discussed in terms of the percolation theory.     

Formation of Cu Nanodots on Diamond Surface to Improve Heat Transfer in Cu/D Composites

Diamond‐dispersed copper matrix (Cu/D) composite materials with different interfacial configurations are fabricated through powder metallurgy and their thermal performances are evaluated. An innovative solution to chemically bond copper (Cu) to diamond (D) has been investigated and compared to the traditional Cu/D bonding process involving carbide‐forming additives such as boron (B) or chromium (Cr). The proposed solution consists of coating diamond reinforcements with Cu particles through a gas–solid nucleation and growth process. The Cu particle‐coating acts as a chemical bonding agent at the Cu–D interface during hot pressing, leading to cohesive and thermally conductive Cu/D composites with no carbide‐forming additives. Investigation of the microstructure of the Cu/D materials through scanning electron microscopy, transmission electron microscopy, and atomic force microscopy analyses is coupled with thermal performance evaluations through thermal diffusivity, dilatometry, and thermal cycling. Cu/D composites fabricated with 40 vol% of Cu‐coated diamonds exhibit a thermal conductivity of 475 W m^?1 K^?1 and a thermal expansion coefficient of 12 × 10^?6 °C^?1. These promising thermal performances are superior to that of B‐carbide‐bonded Cu/D composites and similar to that of Cr‐carbide‐bonded Cu/D composites fabricated in this study. Moreover, the Cu/D composites fabricated with Cu‐coated diamonds exhibit higher thermal cycling resistance than carbide‐bonded materials, which are affected by the brittleness of the carbide interphase upon repeated heating and cooling cycles. The as‐developed materials can be applicable as heat spreaders for thermal management of power electronic packages. The copper‐carbon chemical bonding solution proposed in this article may also be found interesting to other areas of electronic packaging, such as brazing solders, direct bonded copper substrates, and polymer coatings.

     

Effect of sulfur and copper amounts in sol–gel precursor solution on the growth, crystal properties, and optical properties of Cu2ZnSnS4 films

Cu₂ZnSnS₄ (CZTS) thin films were deposited by sol–gel spin coating using precursor solutions prepared with copper acetate, zinc acetate, tin chloride, and thiourea in methanol and ethylenediamine followed by sulfurization. Sol–gel precursor solutions were prepared with different amounts of sulfur and copper, and their effects on film growth, crystal properties, and optical properties of CZTS films were investigated. CZTS film thickness increased with the amount of metal salt in the precursor solution. This is attributed to an increase in solution viscosity and a decrease in the solution density/viscosity ratio. All CZTS thin films exhibited kesterite structures with absorption coefficients larger than 10⁴ cm^?1 in the visible region. Band gap energy increased with increasing amounts of sulfur and decreasing amounts of copper. The blue shift of the band gap is attributed to changes in the degree of p–d hybridization related to Cu d- and S p-levels. The role of sulfur and copper on Hall mobility and carrier concentration was investigated. By optimizing the metal salt ratio in the precursor, CZTS film with a resistivity of 5.3 × 10^?2 Ωcm were prepared.     

Structural,optical, and electrical properties of ZnTe:Cu thin films by PLD

In this work, ZnTe and ZnTe:Cu films were obtained by pulsed laser deposition using the co-deposition method. ZnTe and Cu₂Te were used as targets and the shots ratio were varied to obtain 0.61, 1.47, 1.72, and 3.46% Cu concentration. Doping of ZnTe films with Cu was performed with the purpose of increasing the p-type carrier concentration and establishing the effect of concentration of Cu on structural, optical, and electrical properties of ZnTe thin films to consider their potential application in electronic devices. According to X-ray diffraction, X-ray photoelectron spectroscopy, UV–visible spectroscopy, and Hall effect results, ZnTe and ZnTe:Cu films correspond to polycrystalline zinc–blende phase with preferential orientation in (111) plane. Optical characterization results indicate that as-deposited films (band gap?=?2.16 eV) exhibit a band gap decrease as function of the increase of Cu concentration (2.09–1.64 eV), while, annealed films exhibit a decrease from 1.75 to 1.46 eV, as the Cu concentration increases. Lastly, Hall effect results show that ZnTe films correspond to a p-type semiconductor with a carrier concentration of 3?×?10¹³ cm^?3 and a resistivity of 1.64?×?10⁵ Ω?cm. ZnTe:Cu films remain like a p-type material and present an increasing carrier concentration (from 3.8?×?10¹⁵ to 1.26?×?10¹⁹ cm^?3) as function of Cu concentration and a decreasing resistivity (from 7.01?×?103 to 2.6?×?10^?1 Ω cm). ZnTe and ZnTe:Cu thin films, with the aforementioned characteristics, can find potential application in electronic devices, such as, solar cells and photodetectors.     

Low-Temperature Plasma Sintering of Inkjet-Printed Metal Salt Decomposition Inks on Flexible Substrates

Due to their complex formulation, conductive nanoparticle inks for inkjet printing are limited in terms of the types of metals and substrates that can be utilized. A new and simplified class of inks called metal salt decomposition (MSD) inks has the potential to introduce a multitude of metals, which can be printed directly onto a wide range of substrates. Here, the use of atmospheric oxygen plasma to develop polycrystalline Au and Pt films at processing temperatures near room temperature (≈33 °C) with excellent conductivities up to 10⁵ S m⁻¹ is demonstrated. The conformal nature of the ink allows metal films to be printed onto a broad range of temperature-sensitive substrates including polymers, papers, and fabric. The Au ink is then used to build a simple light-emitting diode circuit showing its flexibility, durability, and long-term stability as deposited thin metal films. Additionally, such inks cost less than one-third the price of similar nanoparticle inks highlighting their overall affordability and good stability.     

Effect of titanium carbide coating on the microstructure and thermal conductivity of short graphite fiber/copper composites

Graphite fiber–Cu composites have drawn much attention in electronic packaging due to its excellent machinability and thermal properties. However, the weak interface bonding between graphite fiber and copper resulted in low thermo-mechanical properties of composites. In this work, a titanium carbide coating with thickness of 0.1 μm or 1 μm was synthesized on the surface of graphite fiber through molten salts method to strengthen interfacial bonding. The enhanced composites present 24–43 % increase in thermal conductivity and achieve the thermal conductivity of 330–365 W m^?1 K^?1 as well as the coefficient of thermal expansion of 6.5 × 10^?6–14 × 10^?6 K^?1. A Maxwell–Garnett effective medium approach on the anisotropic short fiber reinforcement with interfacial thermal resistance was established. The obtained enhancement was in good agreement with the estimates. The results suggest that the major factor that influences the thermal conductivities is not the interfacial thermal resistance but the low thermal conductivity of fiber in transversal direction when a well interfacial bonding is obtained.     

Finite element simulation and experimental research on ZnO:Al by magnetron sputtering

Aluminum doped zinc oxide (ZnO:Al) thin films are suitable for the use as transparent conductive electrode in copper indium gallium selenide Cu(In,Ga)Se₂ thin film solar cells. The resistivity and film quality of ZnO:Al deposited on soda lime glass is nonuniform in magnetron sputtering process. According to the measurement results of magnetic field on the top of the target, obvious magnetic field distribution nonuniformity is observed along the vertical and horizontal directions respectively. With the longer distance between target and substrate, the magnetic field intensity becomes lower and flatter between the two magnet poles. Based on the simulation results by finite element analysis, it is verified the nonuniformity of magnetic field distribution influences the probability of Ar⁺ particles collision and the deposition of zinc oxide (ZnO) particles in different regions on substrate. The higher resistivity of ZnO:Al films is obtained where the magnetic field intensity is stronger.     

Effect of the different shapes of silver particles in conductive ink on electrical performance and microstructure of the conductive tracks

The electrical performance of the ink-jet printed conductive tracks composed of silver particles was investigated. Three different shapes silver particles were synthesized via chemical reduction method in the presence of poly vinyl pyrrolidone, and then they were used to study the shape influence on the electrical property and thermal stability of the conductive tracks. The resistivity variation and microstructure of the silver conductive tracks was monitored as a function of fillers content using a four-point probe and scanning electron microscopy as well as thermal analysis. In addition, we proposed the possible formation mechanism of conductive tracks with different fillers. It demonstrated that the conductive tracks filled with silver nanorods and nanoparticles could achieve the volume electrical resistivity of ~3.2?×?10^?5?Ω?cm after sintering at 160?°C for 15?min. Finally, we fabricated highly conductive silver patterns on a glass substrate by ink-jet printing.     

超高分子量聚乙烯基复合材料导热性能研究

采用纳米铜作为子颗粒,利用颗粒复合化系统,以机械冲击的方法将纳米铜颗粒嵌入式包覆于超高分子量聚乙烯颗粒(UHMWPE)表面,利用热压成形技术制备导热型复合材料。采用导热系数测定仪测试其导热系数,分析纳米铜添加量对导热效果的影响。结果表明:在相同的实验条件下,当纳米铜添加质量分数为6.8%时,复合材料的导热系数达到了0.85 W/(m.K),比纯UHMWPE提高了124%。     

Impact of different coating processes of microfibrillated cellulose on the mechanical and barrier properties of paper

This study presents a comparison of the mechanical and barrier properties of papers coated with microfibrillated cellulose (MFC) by two different coating processes: (i) bar coating and (ii) size press. Due to the high water content of MFC, water-treated papers were taken as references to highlight the effects of MFC on the properties of papers. Structural, mechanical and barrier properties of the ensued materials were performed respectively with SEM, tensile and stiffness testers, and air and oxygen permeability equipments. The properties of the water-treated papers were considerably damaged compared to those of the base paper that underlined the negative impact of both coating processes on the papers structure. With MFC, the air barrier and the bending stiffness were considerably improved (+90 and +50 % respectively), especially when the bar coating was used, i.e. with 7 g m^?2 of MFC. Size press was indeed not able to considerably improve papers properties as the MFC coat weight barely reached 4 g m^?2 resulting from ten successive MFC layers.     

Thermal conductivity improvement of copper–carbon fiber composite by addition of an insulator: calcium hydroxide

The effects of adding calcium hydroxide (Ca(OH)₂) to a copper–CF (30 %) composite (Cu–CF(30 %)) were studied. After sintering at 700 °C, precipitates of calcium oxide (CaO) were included in the copper matrix. When less than 10 % of Ca(OH)₂ was added, the thermal conductivity was similar to or higher than the reference composite Cu–CF(30 %). A thermal conductivity of 322 W m^?1 K^?1 was measured for the Cu–Ca(OH)₂(3 %)–CF(30 %) composite. The effects of heat treatment (400, 600, and 1000 °C during 24 h) on the composite Cu–Ca(OH)₂(3 %)–CF(30 %) were studied. At the lower annealing temperature, CaO inside the matrix migrated to the interface of the copper matrix and the CF. At 1000 °C, the formation of the interphase calcium carbide (CaC₂) at the interface of the copper and CFs was highlighted by TEM observations. Carbide formation at the interface led to a decrease in both thermal conductivity (around 270 W m^?1 K^?1) and the coefficient of thermal expansion (CTE (10.1 × 10^?6 K^?1)).     

Effect of carbon nanotubes shape on the properties of multiwall carbon nanotubes/polyethylene flexible transparent conductive films

Transparent conductive material is used in a wide range of applications and is particularly interesting. In the present work, a series of multiwall carbon nanotubes/low density polyethylene nanocomposites with different carbon nanotubes were prepared via solution casting method. The optical transparency, morphology, and resistivity of transparent conductive films have been characterized by using UV–Vis Spectrophotometer, Field emission scanning electron microscope and Multimeter, respectively. Their electrically conductive and optically transparent properties were studied and compared. The result showed that thinner and longer multiwall carbon nanotubes were more suitable for the fabrication of flexible transparent conductive nanocomposites. The sample filled with 1 wt% of T.1 (outside diameter <8 nm, length 10–30 μm) had good transparent conductive properties (volume conductivity of 3.12 × 10^?3 S m^?1 and optical transmittance of 62.8 % at the light wavelength of 600 nm). The high volume conductivity and optical transparency demonstrated that such kind of nanocomposite films had favorable potential in the applications from electromagnetic interference shielding to transparent electrodes.     

Effect of different copper fillers on the electrical resistivity of conductive adhesives

The effects of different copper fillers with different morphology and particle size have been studied in terms of electrical resistivity and thermal stability on the electrically conductive adhesives. The copper fillers used in this study were prepared by wet chemical reduction, electrolytic and gas atomization method, respectively. The as cured ECAs filled with different type of Cu fillers showed significant difference in electrical resistivity. Cu filler with smaller particle size showed higher packing density and larger surface area, which would enhance formation of conductive channels and increased conductive network in the ECAs, leading to a lower electrical resistivity. In addition, thermal stability of the ECAs were investigated under high temperature exposure at 125 °C and high humidity aging at 85 °C/85% RH for 1,000 h. Results showed that ECAs with Cu fillers of relatively small particle size and rough particle surface have excellent thermal stability due to enhanced adhesion and contact area between Cu fillers and the polymer matrix. A very low resistivity at an order of magnitude of 10^?4 ?? cm could be maintained for these ECAs after 1,000 h at 125 and 85 °C/85% RH.     

Dependence of the properties of copper zinc tin sulfide thin films prepared by electrochemical deposition on sulfurization temperature

Copper zinc tin sulfide (CZTS, Cu₂ZnSnS₄) is a low band gap semiconductor that is attractive for use in solar cells. We investigated the dependence of the structure and properties of CZTS thin films on the temperature used to sulfurize precursor thin films composed of copper, zinc and tin fabricated by electrochemical deposition. The precursor films were sulfurized in a furnace with three zones, which allowed fine control of the sulfurization temperature between 250 and 400 °C. X-ray diffraction and Raman spectroscopic measurements confirmed that the films were composed of CZTS following sulfurization. The grain size and crystallinity of the films increased with sulfurization temperature. The composition of CZTS also varied with sulfurization temperature. The proportions of Cu and Zn increased while that of Sn decreased with increasing sulfurization temperature. Absorption and reflectance spectra revealed that the absorption coefficients and band gaps of the CZTS films varied with sulfurization temperature between 3–4.1 × 10⁴ cm^?1 and 1.4–1.53 eV, respectively. Solar cells containing CZTS sulfurized at 400 °C showed a maximum efficiency of 2.04 %, which was attributed to the higher crystallinity and larger grain size of CTZS compared with thin films sulfurized at lower temperatures. Our results show that control of sulfurization temperature is an important factor in optimizing the performance of CZTS thin films in solar cells.     

Characterization of aluminum-doped zinc oxide thin films by RF magnetron sputtering at different substrate temperature and sputtering power

In this study, transparent conductive Al doped zinc oxide (ZnO: Al, AZO) thin films with a thickness of 40 nm were prepared on the Corning glass substrate by radio frequency magnetron sputtering. The properties of the AZO thin films are investigated at different substrate temperatures (from 27 to 150 °C) and sputtering power (from 150 to 250 W). The structural, optical and electrical properties of the AZO thin films were investigated. The optical transmittance of about 78 % (at 415 nm)–92.5 % (at 630 nm) in the visible range and the electrical resistivity of 7 × 10^?4 Ω-cm (175.2 Ω/sq) were obtained at sputtering power of 250 W and substrate temperature of 70 °C. The observed property of the AZO thin films is suitable for transparent conductive electrode applications.     

Exciting Dilute Magnetic Semiconductor: Copper-Doped ZnO

The present study is focused on the copper-doped ZnO system. Bulk copper-doped ZnO pellets were synthesized by a solid-state reaction technique and used as target material in pulsed laser deposition. Thin films were grown for different Cu doped pellets on sapphire substrates in vacuum (5×10^?5 mbar). Thin films having (002) plane of ZnO showed different oxidation states of dopants. M–H curves exhibited weak ferromagnetic signal for 1–3 % Cu doping but for 5 % Cu doped thin film sample showed the diamagnetic behavior. For deeper information, thin films were grown for 5 % Cu doped ZnO bulk pellet in different oxygen ambient pressures and analyzed. PL measurement at low temperature showed the emission peak in thin films samples due to acceptor-related transitions. XPS results show that copper exists in Cu²⁺ and Cu⁺¹ valence states in thin films and with increasing O₂ ambient pressure the valence-band maximum in films shifts towards higher binding energy. Furthermore, in lower oxygen ambient pressure (1×10^?2 mbar) thin films showed magnetic behavior but this vanished for the film grown at higher ambient pressures of oxygen (6×10^?2 mbar), which hints towards the decrease in donor defects.     

Ultrahigh Conductive Copper/Large Flake Size Graphene Heterostructure Thin‐Film with Remarkable Electromagnetic Interference Shielding Effectiveness

To guarantee the normal operation of next generation portable electronics and wearable devices, together with avoiding electromagnetic wave pollution, it is urgent to find a material possessing flexibility, ultrahigh conductive, and superb electromagnetic interference shielding effectiveness (EMI SE) simultaneously. In this work, inspired by a building bricks toy with the interlock system, we design and fabricate a copper/large flake size graphene (Cu/LG) composite thin film (≈8.8 μm) in the light of high temperature annealing of a large flake size graphene oxide film followed by magnetron sputtering of copper. The obtained Cu/LG thin‐film shows ultrahigh thermal conductivity of over 1932.73 (±63.07) W m^?1 K^?1 and excellent electrical conductivity of 5.88 (±0.29) × 10⁶ S m^?1. Significantly, it also exhibits a remarkably high EMI SE of over 52 dB at the frequency of 1–18 GHz. The largest EMI SE value of 63.29 dB, accorded at 1 GHz, is enough to obstruct and absorb 99.99995% of incident radiation. To the best of knowledge, this is the highest EMI SE performance reported so far in such thin thickness of graphene‐based materials. These outstanding properties make Cu/LG film a promising alternative building block for power electronics, microprocessors, and flexible electronics.     

Structural,optical, photocurrent and mechanism-induced photocatalytic properties of surface-modified ZnS thin films by chemical bath deposition

ZnS thin films were prepared by chemical bath codeposition using ZnSO₄–ZnCl₂ or Zn(CH₃COO)₂–ZnCl₂ as zinc ion sources. The presence of SO₄ ^2? favors the heterogeneous growth of ZnS thin film. The coexistence of two zinc salts impedes the formation of homogeneous precipitation and improves the growth rate of ZnS film. XRD and HRTEM results show that all the samples exhibit the cubic structure. EDS analysis shows that Zn/S atom ratios from the codeposition are closer to 1:1 than those deposited from a single zinc salt, and ZnS thin films of S3 and S7 are very uniform without stirring. FTIR reveals that –NH₂ group as a surface modifier is adsorbed on the surface of ZnS nanoparticles. Raman spectra further reveal that S3, S4 and S7 form the ZnS films, and ZnO phase is present in short or middle range of the S6 nanocrystal, indicating that different amounts of zinc salts affect the structure of ZnS films significantly after three 2.5 h deposition cycles. The grain sizes determined by FESEM are inversely proportional to RMS determined by AFM. The band gap values of ZnS thin films agree well with the results of HRTEM. The photocurrent responses of different samples are similar, indicating that different amounts of zinc salts have little effect on the photocurrent of ZnS films. The photocatalytic performance of S6 and S8 is much better than that of S1–S5. S6 decomposes 65 % of methyl orange within 3 h, and its K value is 4.78 × 10^?1 h^?1. The photocatalytic performance is induced by the growth mechanism, which determines the grain size of ZnS thin film. The tendency of grain sizes of ZnS films agrees well with that of photocatalytic performance, especially under the clusters by clusters deposition.